1. Field of the Invention
The present invention relates to an integrated circuit anti-electrostatic discharge technique, and more particularly to a Lateral Semiconductor Controlled Rectifier with annular structure. This annular structure has a smaller layout size and provides better protection against electrostatic discharge.
2. Description of the Related Art
Due to the improvement of semiconductor technology, the size of CMOS devices (or components) have decreased to the level of sub-micrometer, and even half-micrometer. Following this trend, the semiconductor devices generally comprise thinner gate oxide layers, smaller transistor channels, sources and the drains with shallower junctions, lightly doped drain (LDD) structures, and are fabricated via the silicided diffusion process. The smaller structures and the use of the silicided diffusion process decrease the robustness of the integrated circuit against the electrostatic discharge (ESD).
The prior art uses the Lateral Semiconductor Controlled Rectifier (LSCR) as an ESD protection circuit to protect the sub-micrometer CMOS integrated circuit from being damaged by ESD. Such an example is disclosed in the U.S. Pat. No. 5,012,317. The top view and the cross-sectional view of a conventional LSCR formed in a P-type semiconductor 10 are shown in FIG. 1 and FIG. 2.
FIG. 1 and FIG. 2 display an N-type well 11 formed on a P-type semiconductor substrate 10, a P-type doping region 12 formed in the N-type well 11, and an N-type doping region 13 formed in the P-type semiconductor substrate 10. The P-type doping region 12, the N-type well 11, the P-type semiconductor substrate 10, and the N-type doping region 13 constitute an LSCR, and serve respectively as the anode, the anode gate, the cathode gate, and the cathode of the LSCR.
Furthermore, the N-type doping region 14 and the P-type doping region 15 are formed in the N-type well 11 and the P-type semiconductor substrate 10 respectively, and serve as the ohmic contact regions of the N-type well 11 and the P-type semiconductor substrate 10. Usually, the anode doping region 12 and the contact region 14 are connected to a pad of an integrated circuit, and the cathode doping region 13 and the contact region 15 are coupled to the VSS power source.
Briefly, the conventional structure of the LSCR has been designed with the layout of strip patterns, as shown in FIG. 2. The anode doping region 12, the cathode doping region 13, the contact region 14, and the contact region 15 have strip structures, and are disposed in parallel and set apart from each other. However, due to the trend of reducing the size of the integrated circuit, it is necessary to decrease the size of the LSCR structure. Therefore, it is an important issue in ESD protection circuit design to reduce the size of the LSCR structure while maintaining the protection of the integrated circuit from ESD.
The present invent provides an SCR device with a polygon structure, thereby economizing the size of the layout and the cost, and maintaining the protection of the integrated circuit from electrostatic discharge.
In order to achieve the above object, the present invention provides a SCR device. The SCR device has at least one annular unit formed on a first conductive type semiconductor substrate. The annular cell comprises a second conductivity type well, a first conductivity type doping region, a second conductivity type contact ring, and a second conductivity type doping ring. The second conductivity type well is in the first conductivity type semiconductor substrate, and the first conductivity type doping region is in the second conductivity type well. The second contact ring is in the second conductivity type well, which is surrounding the first conductivity type doping region. The second doping ring is in the first conductivity type semiconductor substrate, which is surrounding the second conductivity type well.
The size of the SCR component can be decreased when the structure formed in an annular shape. Furthermore, the symmetrical structure allows the current through the structure to be increased. The use of the SCR component as the electrostatic discharge protection circuit will therefore increase the protection of the integrated circuit from electrostatic discharge.
Furthermore, the present invent provides a SCR component, which has at least one annular cell formed on a first conductivity type semiconductor substrate and comprising: a second conductivity type floating well, a first conductivity type doping region, and a second conductivity type doping ring. The second conductivity type floating well is formed on the first conductivity type semiconductor substrate, the first conductivity type doping region is formed on the second conductivity type floating well, the second conductivity type doping ring is formed on the first conductivity type semiconductor substrate, which is surrounding the second conductivity type floating well.
Because there is no contact region set on the second type conductivity well, the present invent can decrease the trigger voltage of the SCR component.